Microporous polymer membranes are staple products in the art of separations of fluid fractions.
Poly(oxy-1,4-phenyleneoxy-1,4-phenylene-carbonyl-1,4-phenylene), more commonly known as poly(etheretherketone), or PEEK, displays advantageous chemical and physical properties for many uses. The high melting point (about 367.degree. C.), high glass transition temperature (about 145.degree. C.), low solubility and high chemical resistance make PEEK a material of choice for separations applications for harsh environments.
PEEK is not known to be affected by common organic solvents at room temperature. PEEK is also resistant to acids and bases with the exception of strong acids in high concentrations. The general insolubility of PEEK, while a useful and advantageous property of a membrane in place, complicates the formation of useful articles including microporous membranes from PEEK.
Polymer film useful as ultrafiltration membranes and reverse osmosis membrane supports are traditionally formed by dissolving the polymer in a solvent, casting the polymer solution on a support as a thin film, followed by coagulation of the polymer by immersion of the support and polymer film into a bath of liquid in which the polymer solvent is miscible, but which is not a solvent for the polymer.
PEEK solubility has been reported in concentrated sulfuric acid (German Patent No. 3,321,860). Membranes have been cast from PEEK and dissolved in concentrated H.sub.2 SO.sub.4. However, the membranes formed are no longer PEEK, but rather have been sulfonated. As a consequence of the change of chemical composition, the membranes no longer display the advantageous properties of PEEK, and are known to swell upon prolonged exposure to water. Bishop, M. T. et al., Macromolecules, 1985, 18, 86.